Impreza 2.5 RS Coupe AWD F4-2.5L SOHC (2001)
Vacuum Brake Booster: Testing and Inspection
Using Gauges
OPERATION CHECK (WITH GAUGES)
CAUTION: When checking operation, be sure to securely apply the hand brake.
Checking with gauges
Connect gauges as shown in Figure. After bleeding air from pressure gauges, proceed to each check.
Air tightness check
1. Start engine and keep it running until a vacuum of 66.7 kPa (500 mm-Hg, 19.69 inch-Hg) = point A is indicated on vacuum gauge. Do not
depress brake pedal.
2. Stop engine and watch the gauge. If the vacuum drop range is less than 3.3 kPa (25 mm-Hg, 0.98 inch-Hg) within 15 seconds after stopping
engine, brake booster is functioning properly. If defective, the cause may be one of those listed below.
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Check valve malfunction
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Leak from vacuum hose
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Leak from the shell jointed portion or stud bolt welded portion
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Damaged diaphragm
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Leak from valve body seal and bearing portion
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Leak from plate and seal assembly portion
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Leak from poppet valve assembly portion
Loaded air tightness check
1. Start engine and depress brake pedal with pedal force of 196 N (20 kgf, 44 lbs.). Keep engine running until a vacuum of 66.7 kPa (500 mm-Hg,
19.69 inch-Hg) = point B is indicated on vacuum gauge while the pedal is still depressed.
2. Stop engine and watch vacuum gauge. If the vacuum drop range is less than 3.3 kPa (25 mm-Hg, 0.98 inch-Hg) within 15 seconds after stopping
engine, brake booster is functioning properly. If defective, refer to "Air tightness check".
Lack of boosting action check
